C++入门笔记

一直对C++感到很恐惧，大学里有C的基础，今天终于鼓足勇气入门C++，先大致了解一下，以后用到的时候再详细深入。

Android中有一些很火的领域比如：音视频、物联网，都会涉及到JNI、NDK的开发，了解C++还是会很有帮助的。

抽象：

#include <iostream>
using namespace std;

class Shape
{
public:
    virtual int getArea() = 0;
    void setWidth(int w)
    {
        width = w;
    }
    void setHeight(int h)
    {
        height = h;
    }

protected:
    int width;
    int height;
};
class Rectangle : public Shape
{
public:
    int getArea()
    {
        return width * height;
    }
};
class Triangle : public Shape
{
public:
    int getArea()
    {
        return (width * height) / 2;
    }
};
int main(void)
{
    Rectangle Rect;
    Triangle Tri;

    Rect.setWidth(5);
    Rect.setHeight(7);
    cout << "Total Rectangle area:" << Rect.getArea() << endl;
    Tri.setWidth(5);
    Tri.setHeight(7);
    cout << "Total Triangle area:" << Tri.getArea() << endl;
    return 0;
}

常量

#include <iostream>
using namespace std;

int main()
{
    const int LENGTH = 10;
    const int WIDTH = 5;
    const char NEWLINE = '
';
    int area;

    area = LENGTH * WIDTH;
    cout << area;
    cout << NEWLINE;
    return 0;
}

#include <iostream>
using namespace std;

#define LENGTH 10
#define WIDTH 5
#define NEWLINE '
'

int main()
{
    int area;
    area = LENGTH * WIDTH;
    cout << area;
    cout << NEWLINE;
    return 0;
}

继承：

#include <iostream>
using namespace std;

class Shape
{
public:
    void setWidth(int w)
    {
        width = w;
    }
    void setHeight(int h)
    {
        height = h;
    }

protected:
    int width;
    int height;
};

class PaintCost
{
public:
    int getCost(int area)
    {
        return area * 70;
    }
};

class Rectangle : public Shape, public PaintCost
{
public:
    int getArea()
    {
        return width * height;
    }
};

int main(void)
{
    Rectangle Rect;
    int area;

    Rect.setWidth(5);
    Rect.setHeight(7);
    area = Rect.getArea();
    cout << "Total area:" << Rect.getArea() << endl;
    cout << "Total paint cost:$" << Rect.getCost(area) << endl;
    return 0;
}

文件读写：

#include <fstream>
#include <iostream>
using namespace std;

int main()
{

    char data[100];

    // 以写模式打开文件
    ofstream outfile;
    outfile.open("afile.dat");

    cout << "Writing to the file" << endl;
    cout << "Enter your name: ";
    cin.getline(data, 100);

    // 向文件写入用户输入的数据
    outfile << data << endl;

    cout << "Enter your age: ";
    cin >> data;
    cin.ignore();

    // 再次向文件写入用户输入的数据
    outfile << data << endl;

    // 关闭打开的文件
    outfile.close();

    // 以读模式打开文件
    ifstream infile;
    infile.open("afile.dat");

    cout << "Reading from the file" << endl;
    infile >> data;

    // 在屏幕上写入数据
    cout << data << endl;

    // 再次从文件读取数据，并显示它
    infile >> data;
    cout << data << endl;

    // 关闭打开的文件
    infile.close();

    return 0;
}

友元函数

#include <iostream>
using namespace std;
class Box
{
    double width;

public:
    friend void printWidth(Box box);
    void setWidth(double wid);
};

void Box::setWidth(double wid)
{
    width = wid;
}

void printWidth(Box box)
{
    cout << "Width of box:" << box.width << endl;
}

int main()
{
    Box box;
    box.setWidth(10.0);
    printWidth(box);
    return 0;
}

命名空间

#include <iostream>
using namespace std;

namespace first_space
{
void func()
{
    cout << "Inside first_space" << endl;
}
} // namespace first_space
namespace second_space
{
void func()
{
    cout << "Inside second_space" << endl;
}
} // namespace second_space
// int main()
// {
//     first_space::func();
//     second_space::func();
//     return 0;
// }
using namespace first_space;
int main()
{
    func();
    return 0;
}

生成实例

#include <iostream>
using namespace std;

int main()
{
    double *pvalue = NULL;
    pvalue = new double;

    *pvalue = 29494.99;
    cout << "Value of pvalue:" << *pvalue << endl;
    
    delete pvalue;
    return 0;
}

多态

#include <iostream>
using namespace std;

class Shape
{
protected:
    int width, height;

public:
    Shape(int a = 0, int b = 0)
    {
        width = a;
        height = b;
    }
    virtual int area()
    {
        cout << "Parent class area:" << endl;
        return 0;
    }
};
class Rectangle : public Shape
{
public:
    Rectangle(int a = 0, int b = 0) : Shape(a, b) {}
    int area()
    {
        cout << "Rectangle class area:" << endl;
        return (width * height);
    }
};
class Triangle : public Shape
{
public:
    Triangle(int a = 0, int b = 0) : Shape(a, b) {}
    int area()
    {
        cout << "Triangle class area:" << endl;
        return (width * height / 2);
    }
};
int main()
{
    Shape *shape;
    Rectangle rec(10, 7);
    Triangle tri(10, 5);
    shape = &rec;
    shape->area();
    shape = &tri;
    shape->area();
    return 0;
}

修饰符

#include <iostream>
using namespace std;

class Line
{
public:
    double length;
    void setLength(double len);
    double getLength(void);
};

double Line::getLength(void)
{
    return length;
}

void Line::setLength(double len)
{
    length = len;
}

int main()
{
    Line line;
    line.setLength(6.0);
    cout << "Length of line:" << line.getLength() << endl;
    line.length = 10.0;
    cout << "Length of line:" << line.length << endl;
    return 0;
}

多线程

#include <iostream>
#include <pthread.h>

using namespace std;
#define NUM_THREADS 5

void *say_hello(void *args)
{
    cout << "Hello Runoob!" << endl;
    return 0;
}
int main()
{
    pthread_t tids[NUM_THREADS];
    for (int i = 0; i < NUM_THREADS; ++i)
    {
        int ret = pthread_create(&tids[i], NULL, say_hello, NULL);
        if (ret != 0)
        {
            cout << "pthread_create error:error_code=" << ret << endl;
        }
    }
    pthread_exit(NULL);
}

指针

#include <iostream>
using namespace std;

int main()
{
    int var1;
    char var2[10];
    cout << "var1变量的地址：";
    cout << &var1 << endl;

    cout << "var2变量的地址：";
    cout << &var2 << endl;
    return 0;
}

C++和Java在语法方面其实有很多想象的地方，毕竟C++也是面向对象的语言